An electronic device may comprise various electronic components (for example, non-volatile memories), which are typically integrated on die of semiconductor material. Each die is housed in a suitable package, which protects the die and at the same time allows access to the die. For this purpose, the package exposes several leads that are electrically connected to terminals of the die (for example, through corresponding connection wires).
The leads are normally of the single connection type, wherein each one of them is connected to a single terminal. However, some leads may also be of the multiple connection type (and in particular, of the double connection type), wherein each one of them is connected to two (or more) terminals. The multiple-connection lead is used to exchange signals in mutual exclusion with each one of its terminals. This allows a reduction of the number of leads of the package, and a reduction of the overall footprint of the entire electronic device.
Typically, an electronic device is subject to various test processes to ensure its correct operation. For example, a continuity test may be used to verify the integrity of the connection wires between the terminals and the leads. This allows sorting the electronic devices (by discarding the ones immediately defective) before performing next tests being more complex (for example, of the parametric or functional type). The continuity test is usually run during an open/short test, which is used to detect open-circuit/short-circuit conditions at the leads of the electronic device. For this purpose, a test current is applied to each lead, and the corresponding voltage is measured. Under normal conditions, the test current causes the turn-on of a diode-based protection structure that is present between the corresponding terminal and a reference terminal (maintained at a reference voltage, or ground, through the corresponding lead), so that the measured voltage takes an expected value equal to a clamping voltage of the protection structure (for example, a supply voltage of the electronic device). On the contrary, if the measured voltage takes a value different from the expected one, and in particular a higher value in the event of open-circuit or a null value in the event of a short-circuit, then the electronic device is detected as defective and is discarded.
However, the known continuity tests are not typically able to detect interruptions of only part of the connection wires to the corresponding terminals of a multiple-connection lead (for example, only one out of two). Indeed, in this case the multiple-connection lead remains connected to the other one of its terminals through the corresponding (intact) connection wire. Therefore, the test current still causes the turn-on of the protection structure of the terminal connected to the lead through the intact connection wire, so that the measured voltage still takes the expected value. Consequently, an electronic device being defective for this reason passes the open/short test in any case, and may be detected (indirectly) only during the next parametric or functional tests.
This causes an increase of the test costs of electronic devices, since it involves the execution of the (complex) parametric or functional tests on such defective electronic devices. Furthermore, it is more difficult (if not impossible) to determine the actual cause of each failure of the parametric or functional tests. In any case, a risk exists that some interruptions of the connection wires might not be detected by the parametric or functional tests in specific situations. All of the above may have a negative effect on the production quality of the electronic devices.
These drawbacks may be particularly important in certain specific conditions. For example, in the case of electronic devices that contain a non-volatile memory of the Few Time Programmable (FTP) type, the electronic devices are supplied by the manufacturers with the non-volatile memories completely erased to be programmed in the field only once by the customers—for example, for applications of the automotive type. As a result, the manufacturers only perform the open/short test of these electronic devices, whereas the functional or parametric tests are performed by the customers after their programming. In this case, the electronic devices being defective because of interruptions of only part of the connection wires to the terminals of a multiple-connection lead may be detected only by the customers during the parametric or functional tests. This may cause the return of the defective electronic devices from the customers to the manufacturers, with a resulting increase of the production costs and a decrease of customer satisfaction.